The needs to develop thermosensitive biodegradable
polymers have been raised in the area of
injectable polymer therapeutics. The aims of this work
are to develop thermosensitive biodegradable poly(organophosphazene)
gels having functional group and characterize
their physicochemical properties such as
thermosensitivity and hydrolytic behaviors. Controlled
thermosensitivity and hydrolytic degradability of polymer
gels were obtained with randomly grafted amphiphilic
poly(organophosphazenes). Hydrophobic L-isoleucine
ethyl ester (IleOEt) and hydrophilic poly(ethylene glycol)
550 or 750 Da (PEG 550 or 750) were substituted along
with relatively small amount of glycylglycine allyl ester
(GlyGlyOALL) which was deprotected into glycylglycine
(GlyGlyOH). By this procedure several neutral (Gly-
GlyOALL) and acidic (GlyGlyOH) poly(organophosphazene)
pairs with same substituent ratio were prepared, in
which the ratio of substituent groups could systematically
modulate their thermosensitive properties. The aqueous
solutions and gels of prepared acidic poly(organophosphazene)
also showed the thermosensitive sol-gel transition
and biodegradation at body temperature, respectively.
Acidic poly(organophosphazene) exhibited much faster
hydrolytic degradation than neutral polymer in the buffer
solutions (pH 7.4) at 37 °C. With systematically regulated
thermo-responsiveness and hydrolytic degradability, the
synthesized poly(organophosphazenes) are expected to be
smart injectable materials having a useful moiety and
further chemically conjugated with various bioactive
molecules for biomedical applications.